The invention relates to a device for compacting loosely packed materials, in particular synthetic materials, comprising a shredder/conveyor rotor body arranged in a casing and rotatably drivable around an axis of rotation and a consecutively arranged extruder with an extruder screw that is arranged rotatably and coaxially to the shredder/conveyor rotor body so that materials supplied to the shredder/conveyor rotor body are conveyed to the extruder screw, whereby they optionally are shredded.
The material to be compacted, usually synthetic material, is supplied into a feeding hopper via suitable conveyor means such as a conveyor belt, a roll feeder, a lifting and tipping device or by manual charging, in which feeding hopper the material is pressed onto the shredder/conveyor rotor body by gravity or by a pressing device. Thereby, the synthetic material is compacted and optionally shredded between rotating knives formed at the periphery of the shredder/conveyor rotor body and stationary knives formed at the casing. At the same time, the compacted/shredded material is continuously conveyed further to the extruder screw in an axial manner.
Such a device is known, for instance, from WO 01/47678 A1. In said device, the discharge-end bearing of the cutting shaft has a negative impact on the conveying effect of the synthetic material. The webs provided for supporting the discharge-end bearing represent a substantial obstacle to the material transport and may lead to a considerable curtailment of the material flow, in particular in case of lightweight and fibrous materials. Furthermore, the maintenance of the bearing is difficult and its replacement, respectively, is hardly possible, since such can only be accomplished if the associated installations have been dismantled completely and/or the cutting shaft has been removed. Moreover, the bearing is exposed to an increased temperature load because of its assembly position, in particular if the associated screw is an extruder screw.
From AT 407971 B, a device is known which solves the above-mentioned problems in that the discharge-end bearing facing away from the drive is formed by the extruder screw itself, whereby a separate discharge-end bearing is completely omitted. However, said solution exhibits a disadvantage in that the cutting forces that occur lead to a very substantial radial strain on the extruder screw and hence to increased wear, in particular if the feed opening of the extruder screw is enlarged by pocket-like expansions which, on the one hand, increase the delivery rate of the extruder but, on the other hand, result in even more increased wear as the screw rests on the webs at selective points. Moreover, the drive-end bearing of the cutting shaft is expensive and can, in a fully functional machine, only be configured as a widely projecting portion. Since wear of the extruder screw cannot be avoided, the distance of the stationary knives as mentioned in said document must therefore be selected to be larger than usual in order to prevent the rotating knives from colliding with the stationary knives. This, in turn, creates an increased thermal load of the material caused by milling and can even result in the melting of the material, in particular in case of thermally sensitive materials such as an LLDPE stretch film.
The actual concept of positioning an extruder screw merely at the inner wall of the casing surrounding it was already known long before the filing date of AT 407971, for instance from the following printed publications: DE 26 56 484 A1, DE 23 51 328 A1, DE 31 19 840 A 1, DE 23 10 463 B2, DE 12 61 661 B.
From JP 2000176935, JP 2001038728, JP 2000169859 (drawings) and from WO 01/47678, a device is known wherein the material is discharged axially from the shredding device and is then delivered to an extruder at an angle of 90° relative to the centre line of the knife-supporting shaft, with the bearing opposite the drive being located at the end of the feed screw and a duct surrounding the feed screw exhibiting a downward-directed opening. One disadvantage of that design is that the material is pressed directly in the direction of the bearing by a compression of the feed screw and hence the sealing of the bearing against dust and impurities will involve substantial expenses and, furthermore, the deflection of the material toward the extruder will cause an additional thermal load of the material, thus leading to increased degradation values.
From EP 0 514 327 A1, a device is known wherein the material is discharged by means of a feed screw arranged underneath the knife-supporting shredding device. However, said feed screw discharges into the open and hence no or only a very slight counterpressure will be built up, and consequently there will also be no deflection of the screw. If in said device an extruder screw was directly connected to the feed screw, the same disadvantages as described above would occur.
In document EP 0 329 934 A2, an extruder with a split extruder screw is disclosed, whereby the individual screw parts are rotatable independently of each other. The screw part being the rear part relative to the discharge opening is configured so as to be hollow and receives in its interior a rotating shaft having its front end connected to the front screw part in a torque-proof manner. The front screw part is supported only by the shaft arranged in the rear screw part by means of an axial bearing. Thus, the rear screw part forms an abutment for the axial bearing of the shaft and hence also an abutment for the front screw part. However, said extruder does not exhibit a separate abutment body for the rear screw part.
All above-mentioned devices have a common disadvantage in that increased deflection forces occur because of the material transfer from the knife-supporting shredding device to the feed or extruder screw, which deflection forces are oriented normally to the centre line of the consecutively arranged shredding and extruder shafts, thus leading to increased wear in the feed area of the extruder or feed screw if an additional discharge-end bearing is omitted, and/or in that the known embodiments of discharge-end bearings lead to substantial curtailments of the material transport or to an increased thermal load of the material.